The present invention generally relates to deposition rings which engage electrostatic chucks in a deposition process for making a semiconductor, and more specifically relates to a deposition ring which includes a cut out on its interior circumferential edge to prevent binding of the deposition ring to an electrostatic chuck during a processing operation, such as during a physical vapor deposition process, wherein a material is deposited onto a semiconductor wafer.
It takes several steps to make a semiconductor. Typically, one of the steps involves depositing a material, such as aluminum, onto a semiconductor wafer. Physical vapor deposition (xe2x80x9cPVDxe2x80x9d) is one process which can be used to make such a deposit onto a semiconductor wafer. During PVD, a robot arm places a semiconductor wafer on an electrostatic chuck in a chamber. A deposition ring is engaged (i.e., in contact) with the edge of the electrostatic chuck, and the engagement of the deposition ring with the electrostatic chuck provides that the material which is to be deposited onto the semiconductor wafer is prevented from depositing onto the electrostatic chuck. Shielding the electrostatic chuck during the deposition process is important because electrostatic chucks can be quite expensive, and depositing a material such as aluminum onto an electrostatic chuck can cause the electrostatic chuck to short or be adversely affected mechanically.
Once the wafer has been placed on the electrostatic chuck in the deposition chamber, and the deposition ring is engaged with electrostatic chuck, the chamber is sealed and the material, such as aluminum, is deposited onto the semiconductor wafer. The nature of the PVD process provides that the material is effectively deposited on everything in the chamber. As such, the material deposits onto, among other things, the semiconductor wafer and the deposition ring. As discussed above, the deposition ring effectively shields the electrostatic chuck during the deposition process, which is important in light of the expense of an electrostatic chuck.
While the use of a deposition ring successfully shields the electrostatic chuck during the deposition process, deposition rings sometimes bind to electrostatic chucks during the deposition process. Thereafter, once the deposition process is finished, attempting to disengage the deposition ring from the electrostatic chuck can result in damage to the electrostatic chuck. As discussed above, causing damage to the electrostatic chuck is to be prevented since, in general, electrostatic chucks are expensive.
Typically, a process kit is used in the deposition process. A process kit may consist of, among other things, shields which are placed in the chamber, as well as the deposition ring. Every once in a while, as a matter of standard practice, the process kit is changed. Specifically, a new process kit is installed, and the old process kit is processed, such as dipped in a bath, in order to remove the deposit on the kit. Thereafter, the old process kit (at least some parts thereof), can be re-used.
As a general rule, the longer a deposition ring is used, the more material becomes deposited thereon. The more material which becomes deposited on a deposition ring, the more prone the deposition ring is to binding to the electrostatic chuck during the deposition process. As such, in order to prevent binding of the deposition ring to the electrostatic chuck during the deposition process, the overall amount of deposition is limited between process kit changes. For example, the life of a process kit may be limited to 400 kilowatt-hours to prevent binding, despite the fact that it would be desirable to use the process kit for much longer, such as for 800 kilowatt-hours.
The theory in limiting the life of a process kit is: the less material (such as aluminum) which is deposited onto a deposition ring, the more effective the deposition ring will shield the electrostatic chuck during the deposition process, and the less likely there will be unacceptable deposition around the outside edge of the electrostatic chuck (i.e., at the juncture with the deposition ring). If there is not significant deposition along the outside edge of the electrostatic chuck, then the deposition ring should not bind with, and should readily disengage from, the electrostatic chuck when the process kit is changed.
While limiting the amount of deposition between process kit changes may reduce the likelihood that there will be binding between the deposition ring and the electrostatic chuck, doing so can be expensive. For example, at five thousand wafer starts per week, process kit costs can amount to as much as $40,000 per month, not including tool downtime which is necessary to perform the required maintenance (i.e., changing of the shields, deposition ring, etc.). Limiting process kit life not only increases cost, but doing so does not address the root cause of the problemxe2x80x94the fact that, due to deficient design, deposition rings are prone to binding to electrostatic chucks during the deposition process.
A general object of an embodiment of the present invention is to provide a deposition ring which does not tend to bind with an electrostatic chuck during a deposition process.
Another object of an embodiment of the present invention is to provide a deposition ring which can be used longer before risking binding of the deposition ring to the electrostatic chuck during the deposition process.
Still another object of an embodiment of the present invention is to provide a method of using a deposition ring to shield an electrostatic chuck during a deposition process.
Briefly, and in accordance with at least one of the forgoing objects, an embodiment of the present invention provides a deposition ring which is configured to contact an edge of a chuck and shield at least a portion of the chuck during a deposition process wherein material is deposited onto an item disposed on the chuck. The deposition ring includes a body, and the body having an interior circumferential edge. The interior circumferential edge includes a surface portion which is configured to engage the edge of the chuck when the deposition ring is engaged with the edge of the chuck, and includes a cut out portion which is configured to be spaced away and not contact the edge of the chuck when the deposition ring is engaged with the edge of the chuck. The cut out provides that the deposition ring does not tend to bind with the electrostatic chuck during the deposition process.
The chuck may be an electrostatic chuck. Preferably, the surface portion of the interior circumferential edge of the deposition ring is proximate the cut out portion. The body of the deposition ring may be circular-shaped. Preferably, when the deposition ring is laid flat, the interior circumferential edge comprises a first, vertical surface, a second, horizontal surface, and a third, vertical surface, wherein the first surface intersects the second surface, and the second surface intersects the third surface. While the first surface comprises the surface portion and is configured to engage the edge of the chuck when the deposition ring is engaged with the edge of the chuck, the second and third surfaces define the cut out portion of the interior circumferential edge of the deposition ring which is configured to be spaced away and not contact the edge of the chuck. Preferably, the third surface is longer than, such as four times longer than, the first surface.